Thread: Advice needed - bowed wood

Timber moves all the time. 7mm is very thin and you would have trouble keeping that flat no matter what you did.
If you need to pre-machine parts then make them oversize. You then have some size to play with when you want to use them.
The best thing to do is use them as soon as you machine them. If you have to leave them for a while they are probably best left on a flat surface with some weight on.
That has been my experience anyway.

Thank you NCArcher that makes good sense. I will try all your suggestions.
I really appreciate your help.
Thank you.

Originally Posted by Featherwood

Hi, I need some advice please if anyone can help.
I had a slab of Tasmanian Blackwood which was 50mm thick x 150mm wide x 1500mm long. I needed a piece 7mm thick x 150mm wide x 200mm long.
After ripping and then putting through the thicknesser to 7mm I stood the piece up on its end for a couple of weeks but it now has a slight bow and is out by a couple of mm each side.
I'm only new to using the thicknesser......is there a trick to making/keeping wide thin boards flat? (I will be needing more) Can I flatten the bowed board I have already cut?
Any help would be greatly appreciated.
Thanks.

Hi Featherwood:

A couple of comments that might help for this piece, and perhaps for future pieces. The finished piece you require is very short (200mm), and considering this would be (or has been) cut from a much longer piece (i.e. 1500mm), do you really mean "bow" along the length of the board, or "cup" which is movement across the grain?

If you mean "cup", then you can take your piece of timber and lay it concave down (i.e. as in like an upsidedown "u", or "concave" for "cave"), and over time the exposed timber will often contract and the cup will come out. Forgive me if you know all this...I certainly don't mean to patronise!

If you meant "bow", then your piece of 1500mm must have really moved a fair bit for you not to be able to get a piece 200mm long out of it, somewhere along its length!

The other point that might be helpful is the best way to store timber, especially timber which has been machined, and that is not standing up on its end, unless it is fully supported. I have been guilty many a time of just leaning a board up against the wall and forgetting about it for a month or two -- gravity does its thing, and the board becomes bowed. If this happens to be the case, you could always try flipping it over and leaving it for another few weeks! I have found timber laid flat, and stickered (i.e. with sticks underneath and between boards) is best. Sometimes I have failed to put enough stickers under a board, and it has bowed (i.e. sagged) just between two stickers! Not good.

Mate, I hope some/any of the above is helpful. Cheers.

Hi LuckyDuck,
Wow! That's really interesting and informative. No, I didn't know any of that. Now that I understand the terminology....it is not bowed....it is cupped.
My original piece of Tasmanian Blackwood is very straight, it was only after machining the small pieces that they cupped.
Thank you so much for your valuable information, it will help me enormously.

Really Grateful,
Featherwood

No worries Featherwood. The magic of these forums is someone is bound to know the answers to our questions, and every once in a long while, we even get to answer the questions of others!

Just another point to keep in mind. I note that you started with 50mm stock and only required 7mm. Would I be correct to assume that you thicknessed the original stock down to 7mm? If so, and besides the fact that a lot of timber went into the dust extractor such heavy thicknessing can expose the inner portion of a board which does not necessarily have the same moisture content as the surface of the board.

A piece which has not been dried thoroughly will be wetter inside than on the surface. Alternatively, a piece which has not stabilised in its current location (say gone from a place of low humidity to a place of high humidity) may actually be drier inside than on the surface.

Further, if you happened to thickness the board predominately on one side of the board, then this "relative" moister content would no longer balance, in that either side of the board has different moister contents.

Some pointers to keep in mind -- again assuming that I am not patronising, which is certainly not my intention:

1. Let boards stabilise for several weeks to several months inside your shop before machining them; even longer if they are not properly dried in the first place. I know, it seems a long time, but sometimes it pays to wait...

2. When machining a board, always try to take the same amount from either side, by flipping the board repeatedly so that you expose the same amount of "new timber" on each side.

3. Due to this moisture issue, it is generally better to try to use boards which are close to the final thickness you require. Obviously this is not always possible. Another reason to do this is that some species have internal cracks (called "checking") and these can be exposed through radical machining (e.g. Jarrah is prone to such checking).

4. Also, if you do have a bandsaw and are able to resaw your 50mm board to yield say a 10mm and a 38mm board (2mm in kerf), your 10mm board would usually cup one way or the other, depending on whether the board is wetter or dryer inside. In general, leave the board under a weight (I use a couple of 20kg weight plates) for a month or so before machinging to your final 7mm.

Anyway, I hope some of this is helpful for the next time... and others might have some other methods of work...

Hi Luckyduck,
Thank you for sharing your wonderful knowledge.
My local specialty timber shop only stocks 40 & 50mm thick slabs of TBW, I couldn't find any thinner.
I did rip the 50mm piece on the table saw first so I ended up with 2 x 24mm thick pieces before putting them through the thicknesser. I do admit I did put them through the thicknesser more on one side than the other.
I have two more slabs of TBW 1 x 40mm, 1 x 50mm thick which have been lying flat on the floor of my shed for about a month or so. Do you think the best thing for me to do would be to rip it into 20mm & 25mm thick boards, then store them flat with sticks in between....then as needed put through the thicknesser and put under weights for a while before use?
I am a carver and normally thick timber is just what I need but I'm changing my style of carving and I'm experimenting with a back board and a base on the carvings so this is all new to me.
Your advice is much appreciated.
Featherwood.

Originally Posted by Featherwood

I have two more slabs of TBW 1 x 40mm, 1 x 50mm thick which have been lying flat on the floor of my shed for about a month or so. Do you think the best thing for me to do would be to rip it into 20mm & 25mm thick boards, then store them flat with sticks in between....then as needed put through the thicknesser and put under weights for a while before use?
I am a carver and normally thick timber is just what I need but I'm changing my style of carving and I'm experimenting with a back board and a base on the carvings so this is all new to me.
Your advice is much appreciated.
Featherwood.

Yes, exactly, you give the timber the best chance of being stable by giving it plenty of time to equalise. My recommendation would be to machine your slabs to within say 5mm of final thickness, and let it sit for as long as possible, but at least a couple of weeks. Then, when you need a piece you can thickness that last couple of mms to correct any further war page, and then go from there. Weights are generally only needed, in my experience, when you are radically resawing or otherwise changing the thickness of a piece. Otherwise, you can just sticker the timber and let it equalise moisture content on all sides.

Obviously, this is just what has worked for me. Others may have a different opinion.

Thank you so much Luckyduck for your invaluable advice. Your words of wisdom are greatly appreciated.
I am no longer in the dark and feel much happier preparing the timber for this and my next project.

Thanks again
Featherwood